Art of coloring aluminum articles



like.

Patented May 14, 1935 UNITED STATES PATENT. OFFICE 2.001.427 b ART orcomma ALUMINUM ARTICLES James Francis Leahy, Fair-haven, Mass., assignorto Atlas Tack Corporation, Fair-haven, Mass., at corporation of New YorkNo Drawing. Application May 14, 1980,

Serial No. 452,525 I 11 Claims.

This invention relates to the art of coloring aluminum or aluminumalloys, being more particularly applicable to fabricated, small aluminumarticles such as buttons, eyelets, and the An object is to make possiblea more economical, uniform, and durable coloring of such articles thanthat effected by the use of: so-called japans, varnishes, and lacquers.Another object is to make possible the handling of a large number ofsuch articles in a batch without requiring any particular arrangement ofthe articles, thereby obviating the trouble and expense incident to thehandling of the individual articles.

I have found that if such articles are superficially oxidized and arethen treated with mordant dyes, insoluble color lakes maybe tenaciouslyfixed in situ on the aluminum base in sufficiently hard and densecondition that they are resistant to the abrasion of handling oruse. Thereaction is evidently analogous to that occurring when textile goods aretreated with mordant dyes, as in such case aluminum oxide or othermetallic oxides are used to fix the dye on the goods.

The superficial oxidation of aluminum may be effected in a great manyways, but I have found that solutions of oxidizing agents, and morespecifically a solution of sodium carbonate and sodium bichromate, notonly effect the desired reaction very quickly, but produce a dense, hardcoating of oxide which is strongly adherent to the aluminum base. Thisoxide is a mixture of both aluminum and chromium oxides, the sodiumbichromate evidently being reduced by the metallic aluminum into anoxide while serving to oxidize the metallic aluminum into an oxide. Inorder to effect, a rapid and uniform coloration of theoxide-coated'base, it is distinctly desirable and in most casesnecessary to use an acid solution of the dye, but only weak ,or slightlyionired acids have been found satisfactory for this purpose.

Various specific examples of procedure falling within the purview ofthe'present invention are possible, but I shall give one example whichhas been found to give eminently satisfactory results on a commercialscale. Aluminum articles, such as buttons, are placed in a suitableperforated container or basket, and the basket then immersed in asolution of about 2% sodium carbonate and about /2% sodium bichromate,preferably at boiling temperature, aselevated temperature serves toaccelerate the reaction. The articles need remain in contact with theboiling solution for only about five to fifteen minutes, at

the end of which time a coating or skin of oxide of the desired depthhas been produced'and little further reaction takes place, probablyowing to the impermeable character of the coating. The basket ofarticles is then removed from the solution and is preferably washed freeof entrained solution; as by dipping into a bath of wash water. It isthen immersed in a bath, preferably at about boiling temperature,containing about 1% of a lake-forming or mordant dye, of the desiredcolor, for instance alizarin red, blue, or green, or a mixture of suchdyes, and about 1% of a weakly ionized acid, such as formic, acetic,lactic, tartaric, boric, or phosphoric aud the articles permitted toremain in contact with the dye for about fifteen minutes, at the end ofwhich time a practically maximum coloration has been efiected. The useof a dye bath at elevated temperature is highly desirable, in that thereaction to form the colored coating is greatly accelerated by increaseof temperature, little reaction taking place at room temperature. Thearticles may then be dried; and, if desired, this may be effected in acurrent of warm air, inasmuch as no visible discoloration takes placeunder such conditions. The insoluble color lake formed on the articlesis resistant to scratching or abrasion, and is characterized by itsdensity, hardness, and tenacity. It is firmly bonded with the aluminumbase, but it can be removed by a hard, sharp instrument. The color lakeresists removal, even by repeated treatment in solutions of alkali orsoap such as are used for laundering purposes, so that aluminum buttonscolored in accordance with my process are especially suitable for use onshirts or other articles of apparel which undergo repeated launderingtreatment. This resistance to removal of the dyed coating by washingfluids is in marked contrast to the ready removability of the uncoloredoxide coating by the same agents. It has been found necessary for thepurpose of developing the desired colored or dyed coating to treat thearticles with the dye solution while the coating of oxide is in a wetand comparatively freshly formed condition as a result of the treatmentwith the oxidizing solution. The superficially oxidized articles shouldhence not be dried or be kept much longer than a day, even if maintainedunder water, for, if they are once dried or allowed to stand for, say, aweek, even under water, there is little or no "color reaction when theyare treated with the dye solution. This charactering step between thetreatment with an oxidizing solution and a dye solution is avoided.

In addition to those advantages already enumerated, my process possessesmerit in that it may be practised with inexpensive apparatus and withlittle consumption ofchemical or dye. The oxidizing and dye baths whichI employ may be reused many times, with the addition of such littlemake-up chemical or dye as has been removed by reaction on the aluminumarticles or by entrainment. Another advantage of my process is that itmakes possible the use of a family of organic dyes which includes alarge variety of colors or tints. While I cannot state with precisionwhat reactions take place in the oxidizing bath, nevertheless it appearsprobable that the sodium carbonate converts the metallic aluminum intothe oxide and that the sodium bichromate favors reaction and is itselfreduced in such a way as to produce an oxide coating having the desiredphysical characteristics. The part played by the acid in the dye bathshas not been ascertained, but it may perform the function of a catalyst,perhaps initially reacting with the aluminum oxide to form salts, which,in turn, react with and fix the dye in the desired insoluble condition.

I claim:

1. A process of coloring aluminum articles, which comprises treatingsuch articles with a solution of sodium carbonate and sodium bichromateto form a coating of aluminum and chromium oxides, and, while thecoating is wet and in freshly formed condition, treating it with asolution of a lake-forming dye containing added weakly ionized acid toform an insoluble color lake on such articles.

2. A process of coloring aluminum articles,

which comprises immersing such articles in a hot solution of about 2%sodium carbonate and about /2% sodium bichromate to form a coating ofaluminum and chromium oxides, and then immersing the coated articles ina hot solution of about 1% of a lake-forming dye and 1% of a weaklyionized acid to form an insoluble color lake on such articles.

3. A superficially colored article, comprising an aluminum base coatedwith an insoluble color lake consisting of the reaction product of mixedaluminum and chromium oxides with a lakeforming dye solution containingadded slightly ionized acid.

, 4. A process of coloring aluminum articles, which comprises treatingsuch articles with a solution of oxidizing agents, and thereaftersubjecting the coated articles to the action of a mordant consisting ofa weakly ionized acid and of a lake-forming dye.

5. A process of coloring oxide-coated aluminum, which comprises treatingthe oxide-coated surface with a dye solution containing a weakly ionizedacid.

6. The method of coloring oxide-coated aluminum, which comprisestreating the oxidecoated surface with a dye solution containing aceticacid.

'I. In a process of coloring aluminum articles, those steps whichcomprise treating the articles with a solution of an oxidizing agent toform a coating of oxide on the articles, and immediately thereaftertreating the freshly coated articles with a dye solution containing aweakly ionized acid.

8. A superficially colored article, comprising an aluminum base coatedwith an insoluble color 'lake comprising the reaction product ofaluminum oxide with a lake-forming dye solution containing addedslightly ionized acid.

9. A superficially colored article, comprising an aluminum base coatedwith an insoluble color lake comprising the reaction product of aluminumoxide with a lake-forming dye solution containing added acetic acid.

10. A process of coloring oxide-coated aluminum, which comprisestreating the oxide-coated surface in the presence of weakly ionized acidwith a dye solution.

'11. A superficially colored article, comprising an aluminum base coatedwith an insoluble color lake comprising the reaction product of aluminumoxide in the presence of weakly ionized acid with a dye solution;

JAMES F. LEAHY.

